Major steps in the calibration process

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Calibration can be summarized by the following six steps:

1. Remove gross overall errors, usually volume errors.
   Large volume errors are usually caused by initial parameter values way out of range, or large errors in the MAP, MAT or MAPE time series.
2. Obtain reasonable simulation of observed baseflow.
   Since the volume of storm runoff is linked to the percolation of water to the lower zone in the SAC-SMA, the proper simulation of baseflow will result in an improved simulation of fast response storm runoff.
3. Adjust major snow model parameters.
   Here, parameters governing the melt rates and volume of snowmelt runoff should be examined.
   
4. Examine SAC-SMA tension water capacities.
   Theses two storages act as thresholds to govern the timing of runoff generation as well as the size of soil moisture deficits that can occur in response to evapotranspiration.
   
5. Adjust parameters governing the generation of fast response or storm runoff.
   The proper separation between baseflow and fast response runoff should be under a wide range of soil moisture conditions.
   
6. Make final adjustments.
   These involve changes to the unit hydrograph, adding in riparian vegetation effects, and adjustments to the evapotranspiration demand function.
   

excerpted from Smith et al, 2000

Several years of historical data should be set aside for verification of model calibration.